1. Field of the Invention
The present invention relates to a workpiece-gripping chuck capable of gripping a workpiece by an opening/closing action of a gripping section, and a method for controlling the same.
2. Description of the Related Art
A workpiece-gripping chuck has been hitherto known, which is attached, for example, to a forward end of a shaft section of a machine tool or the like, and which grips a workpiece, such as various types of parts, by causing a gripping section to effect an opening/closing operation by supplying a pressure fluid to the gripping section.
The present applicant has suggested a workpiece-gripping chuck capable of gripping a workpiece by means of opening and closing a gripping section through a pressurizing action of a pressure fluid (see, Japanese Laid-Open Patent Publication No. 7-328977).
The workpiece-gripping chuck comprises a body provided with a pair of ports for supplying the pressure fluid, wherein a piston, which is provided in the body, is displaced in an axial direction under the pressurizing action effected by the pressure fluid. Accordingly, a shaft section of the piston rotates a pinion, which is rotatably supported by the body through the aid of a rack formed on a side surface thereof. A pair of gripping members is rotatably supported by the rotary shaft of the pinion respectively. The gripping members are displaced in a direction so as to approach one another, or to separate from each other, about the center of the rotary shaft due to the rotary action of the pinion. Accordingly, the gripping members are displaced in a direction so as to approach one another, and the workpiece is gripped between the gripping members. (See, for example, Japanese Laid-Open Patent Publication No. 7-328977.)
An air-driving type of workpiece-gripping chuck, as disclosed in Japanese Laid-Open Patent Publication No. 7-328977, in which the pair of gripping members are opened/closed under a pressurizing action of the pressure fluid, is advantageous in that a large gripping force is obtained through use of the pressure fluid. However, it is difficult to arbitrarily control the opening/closing amount of the gripping members. In other words, the workpiece-gripping chuck is capable of performing only operations of fully opening or fully closing the gripping members.
In recent years, a workpiece-gripping chuck has been sought, which provides a predetermined amount of gripping force when a workpiece is gripped, and in addition, which is capable of freely controlling the opening/closing amount of the gripping members depending on the shape of the workpiece and/or the environment of use.